1. Field of the Invention
The present invention relates to an extendable shaft for use, for example, in steering assembly for vehicles.
2. Description of Related Art
An extendable shaft includes a type which includes a first tubular shaft section and a second shaft section inserted and fitted in the first tubular shaft section. The first and the second shaft sections are engaged with each other via spline fit so as to be slidably movable relative to each other.
Some of the conventional extendable shafts have a play elimination function for obviating the occurrence of play at a spline fit portion. Specifically, the aforesaid first shaft section is formed with a plurality of slits at an end thereof, and the slits are opening toward an opening end and extending for a predetermined length along an axial direction. This involves the formation of a plurality of cantilevered tongues, elastically deformable, between the slits.
In order to prevent the occurrence of play at the spline fit portion, a clamping member for elastically clamping the aforesaid tongues is fitted on an outer periphery of the plural tongues. A clamping force of the clamping member elastically deforms the tongues, thereby reducing the diameter of the end of the first shaft section (see, for example, FIG. 1 of Japanese Utility Model Publication No.63-17862, FIG. 2 of Japanese Unexamined Patent Publication No.62-106127).
As long term changes become heavier, the wear of spline teeth increases. If the tongues are elastically yielded in an insufficient amount relative to the amount of wear, play occurs at the spline fit portion.
Hence, it may be contemplated to increase the clamping force of the clamping member. However, the increase of the clamping force results in an increase of slide resistance at the spline fit portion between the first and the second shaft sections.
It is an object of the present invention to provide an extendable shaft adapted for the reduction of the slide resistance at the spline fit portion and ensuring a long term prevention of the occurrence of play.